Prowler proof latch means



April 4, 7 A. N. MACDONALD PROWLER PROOF LATCH MEANS 2 Sheets-Sheet 1 IN VENTOR.

Filed Oct. 21, 1965 .ARc/v/E N MACDONALD April 4, 1967 A. N. MACDONALD 3,312,490

PROWLER PROOF LATCH MEANS Filed Oct. 21, 1965 2 Sheets-Sheet 2 INVENTOR,

ARCH 1E N. MACDONALD United States Patent Filed Oct. 21, 1965, Ser. No. 505,596 I 2 Claims. (Cl. 292-153) This application is a continuation-in-part of previously filed and copending application Ser. No. 395,830 filed Sept. 11, 1964, since abandoned.

This invention concerns method and means for selectively preventing normal operation of a door latch or the like as necessary to open a door. More particularly, this invention concerns an attachment of improved effectivenesses, ease and economy of manufacture, adaptability and simplicity which may be added to existing door latches of the familiar household type to render the latch tamper proof.

Door latches of the familiar type used on houses, apartments, stores and other buildings, both on outer and inner walls, typically include no means to prevent a person having unauthorized possession of a key from operating the latch in the normal manner to gain access to the building or some portion thereof. Thus, when an apartment or house is rented to tenants from time to time who have additional keys made during their period of occupancy, it becomes necessary for landlords to change locks on the rented property to prevent such keys possessed by previous occupants from being used to gain unauthorized access when the property is rented to new tenants. Alternatively, separate bolts or chain guards must be added to safeguard doors against opening, but such devices are often costly and difficult to install due to the shapes, sizes and materials of construction of many doors and door jambs.

Moreover, even when an individual such as a prowler or burglar has no key, most door latches are susceptible to opening by use of thin blades or the like inserted between the door and its adjoining door jamb to push the bolt or latching member out of its aligned cavity by a wedging or camming action, even when the latch is supposedly in locked condition. Thus, the familiar household types of door locks and latches in common use modernly are not burglar proof, and include no means to render them selectively inoperable against tampering or unauthorized operation by anyone wishing to gain access through any door equipped 'with such looks or latches.

Accordingly, it is a principal object of this invention to provide means to prevent disengagement of a door latch or the like from locking engagement by normal means including a key which would otherwise be operable to disengage such latch from looking engagement.

It is a further object in this case to provide means as set forth in the above object adapted for manufacture and installation with improved ease and economy, and regardless of the shape or materials of construction of the door, door jamb, molding pieces or adjacent walls.

It is a further object in this case to provide means of improved simplicity and economy to convert a latch 'ice closed herein will become apparent upon a close reading of the following detailed descripion of certain illustrative embodiments of the inventive concept, reference being had to the accompanying drawings, wherein:

FIGURE 1 shows a plan cross-sectional view of a hinge mounted door and related door jamb of the familiar household type which may incorporate the novel teachings disclosed herein,

FIGURE 2 shows a general perspective view, partly fragmented, of a door latch and adjacent door jamb in the unlatched condition incorporating the inventive principles taught herein,

FIGURE 3 shows a general perspective view corresponding essentially with FIGURE 2 but illustrating a slightly different structural modification of the same inventive principles embodied in FIGURE 2,

FIGURES 4 and 5 show general perspective views of a different form or embodiment of the inventive concept with latch holding means engaged and disengaged with a latch bolt,

FIGURE 6 shows a perspective exploded view of a further and slightly different modification of the embodiment of FIGURES 4 and 5, and

FIGURE 7 shows the structure of FIGURE 6 in assembled operative relationship.

Referring to the drawings described above and particularly to FIGURE 1, it may be seen that the invention in this case is adapted for use with conventional door latches of the general type shown mounted on a household door 10. Door 10 may be an inner door between two rooms of a house, for example, or an outwardly facing door such as to provide access into a house from outside thereof. For clarity of explanation herein, the invention will be described in relation to its use on outwardly facing doors, whereby door 10 may be illustratively considered to have a side 12 facing the interior of a house or apartment and a side 14 facing exteriorly. Door 10 is pivotally mounted by a plurality of hinges 16 along one edge 18 of the door and an adjacent portion 20 of a door jamb adapted for structural cooperation with door 10 in the familiar manner. Edge 22 of door 10 opposite from the location of hinges 16 is aligned with another portion 24 of the door jamb when door 10 is in the fully closed position, as seen in FIGURE 1. An elongate bolt or latch member 26 extending outwardly from edge 22 of door 10 aligns with a cavity 28 in from the non-locking type to one which may be eifectivedoor jamb portion 24 (see FIGURE 2) and enters the cavity to hold door 10 closed. A pair of door knobs 30 and 32 are provided on door 10 and operatively related to withdraw latch member 26 out of cavity 28 and into edge 22 of the door when opening door 10.

It is characteristic of hinge mounted doors such as door 10 that a space or gap 33 between the door edge 22 and the confronting surface of the adjoining door jamb is provided as shown in FIGURE 1 to permit arcuate movement of door 10 about a pivot axis through hinges 16. Thus, edge 22 moves generally along a path indicated by broken line 34 in FIGURE 1 during opening or closing movement of door 10. To provide the necessary clearance between edge 22 and confronting portion 24 of the door jamb for permitting such arcuate movement, distance A across gap 33 is typically from to /s inch across, or more in the case of abnormally thick doors. It is this gap or space 33 which renders every lock of the typical and familiar type shown in FIGURE 1 and discussed above especially vulnerable to tampering by prowllers or the like, as explained in greater detail below.

Referring to FIGURE 1, it may be seen that portion 24 of the common household door jamb is typically provided with stop means to limit the over travel of edge 22, during closure of door 10, beyond the position in which latch member 26 is aligned with cavity 28. The

stop means normally consist of a separate wooden strip 35 afiixed to door jamb portion 24 by a plurality of brads or thin wire nails. When strip 35 isslightly separated away from door jamb portion 24 as by prying, gap 33 is exposed whereby access to latch member 26 may be had by reaching a wire, blade or other implement from outside door through gap 33 Referring to FIGURE 2, it may be seen that elongate latch member 26 in a typical household latch mechanism, is mounted and arranged for relative linear movement along its long axis. Usually such movement may be caused in three principal ways: by door knobs 30, 32; or by a key (not shown); or by force applied to cam surface 36 on the distal end of latch member 26 to push the stated member inwardly toward edge 22 of door 10. The last stated method may occur automatically during closing movement of door it) in the absence of force applied to either of knobs 36 or 32. Thus, latch member 26 is usually spring biased toward the extended position shown in FIGURES l and 2, for example, whereby closure of door 10 results in contact between cam surface 36 on latch member 26 and a striker plate 40 affixed to door jamb portion 24. After such contact is initially established, continued movement of edge 22 of door 10 along line 34 toward the fully closed position will cause striker plate 40 to apply force to latch member 26 overcoming the bias thereof and pushing member 26 into edge 22 of the door by a camming action. When door 10 is in the fully closed position, the distal end of latch member 26 will be aligned with cavity 28, whereby the stated outward bias of member 26 will cause its end portion to enter the cavity in latching relationship whereby door It) will be held closed until external force is applied to withdraw member 26 from cavity 28. Of the three ways to apply such force already mentioned, the most significant from the standpoint of latch vulnerability to prowlers is the application of force directly upon cam surface 36 of latch member 26. Such force may often be applied by inserting a thin blade, nail, or the like as denoted by reference numeral 58 in FIGURE 1 into gap 33 and pushing the tip of such blade, nail, etc, against cam surface 36 on the distal end of latch member 26 to cam the member back toward edge 22 of door 10. It is an unfortunate characteristic of virtually all household latches in common use modernly that the latch or bolt represented by member 26 in FIGURES 1 and 2 of this case may be pushed into edge 22 of door 10 by direct force applied to the distal end thereof even though external force be applied on both door knobs 30 and 32 to hold them against rotation, and even though a key be used to lock the latch mechanism again-st operation by the door knobs. It is a further characteristic of typical household door latches that no grooves, detents, holes, or the like are provided on the latching member corresponding to member 26 in FIGURES l3 of this case, and no means to prevent independent movement of such member with respect to its operatively associated door knobs. Latch elements corresponding with member 26 in common use today are perfectly smooth surfaced along that portion thereof which extends beyond the door edge and into the operatively related cavity of the confronting door jamb surface.

The invention disclosed herein contemplates means independent of knobs 30 and 32 for selectively preventing withdrawal of latch member 26 from cavity 28 by application of any amount of force in any manner even including a key to unlock the latch mechanism. Considering first the embodiment shown in FIGURE 2, it may be seen that the invention may include independent holding means in the form of slide element 42 for selectively holding latch member 26 in substantially constant relationship with edge 22 of door 16 when the member 26 is in the extended or latching position. Slide element 42 is of relatively thin sheet and elongate form having an edge 44 movable into or out of contacting relationship with a shallow groove or notch 46 cut into latch member 26 at a location spaced inward-1y from the outermost tip 48 thereof. Notch or groove 46 may be cut into the latch member corresponding to member 26 in any existing household door latch by use of an ordinary hacksaw blade. Alternatively, groove 46 may be formed in member 26 in any convenient manner at the time of its initial manufacture. Many different ways to support slide element 42 for selective positioning relative to door 10 will be obvious to those skilled in the art, such variations not significantly changing the results or advantages of the overall concept disclosed herein. However, FIGURE 2 illustratively shows slide element 42 supported on a bracket 50 of right-angle form iaflixed to door 10 by appropriate means such as a plurality of screws 52. A pair of rivets or studs 54 are atfixed to bracket 50 and arranged to extend through an elongate slot 56 in slide element 42. Alternatively, the rivets may be aflixed to slide element 42 and slot 56 may be provided in bracket 50.

From the description of structure set forth above, it will be understood that slide element 42 may be moved laterally relative to door 10 and bracket 50, to position edge 44 of element 42 in operative engagement with groove 46, or to withdraw edge 44 therefrom. With edge 44 withdrawn from the groove, latch member 26 may be freely moved along its main axis such as to withdraw distal end 36 thereof from cavity 28 by the action of either knob 30, 32, or by a key (not shown), or by force applied to cam surface 36 using a blade or nail in the manner discussed hereinabove. However, when slide element 42 is selectively positioned by sliding the same so that edge 44 enters and operatively engages groove 46, movement of latch member 26 by any and all means such as necessary to disengage the distal end of member 26 from cavity 28 when door It} is fully closed, is effectively prevented. Thus, if door It and blade 58 is inserted through gap 33 from the exterior side 14 of door 16 to contact cam surface 36 and move latch member 26 out of latching engagement with cavity 28 in order to open door 10 by stealth when the door is closed and locked, such unlatching movement of member 26 will be prevented by the holding action of slide element 42 engaging groove 46.

It is of further importance in the inventive concept of this case that slide element 42 is constructed and arranged in relationship with latch member 26 so as to prevent element 42 from being movable out of holding position in relation to groove 46 by anyone reaching any tool or implement through gap 33 from the exterior side 114 of door It Thus, slide element 42 as seen from FIGURE 2 is supported on bracket 50 in a position of substantial horizontal alignment with latch member 26 so that blade 58 moving in a direction defined by the long axis of the blade toward cam surface 36 cannot contact member 26. Moreover, any wire hooks or the like inserted through gap 33 cannot engage any notches or discontinuities in slide member 42 to push the same out of holding position relative to groove 46, since all such discontinuities may be substantially avoided as accomplished in the structural embodiment shown by FIGURE 2, for example.

Referring to FIGURE 3, a different structural embodiment of the same inventive principles involved in the modification shown by FIGURE 2 may be seen. Thus, instead of a slidable member mounted on a bracket, FIGURE 3 shows independent holding means in the form of rotatable element 60 for selectively holding latch member 62 in substantially constant relationship with edge 22 of door 10. The latch mechanism shown in FIGURE 3 may correspond in function with that shown in FIGURE 2, hence its operation needs no additional explanation. It will be understood that, while latch member 62 is shown as square in cross-sectional shape, it could .be substantially round as some latches are, since the inventive concept in this case does not require. any paroc ar shape. for such member.

As in the case of latch member 26 in FIGURE 2, member 62 in FIGURE 3 is provided with a groove 64 adapted to receive a first engageable edge 66 of holding member 60. Member 60 is pivotally mounted on the coverplate 72, which typically surrounds latch member 62 in a common household door latch, by the same screw 74 which normally holds coverplate 72 on door 10. To this end, the mounting hold in member 60 may be countersunk to permit screw '74 to be flush with the surface of member 60 as shown in FIGURE 3. Due to the foregoing manner of attachment for rotatable member 60 on edge 22 of door 10, it will be understood that member 60 is rotatable about a pivot axis through the center of screw 74 to lock door effectively from either side 12 or 14 thereof. However, due to the interference offered by door stop means 35 shown in FIGURE 1, for example, it will be understood that member 66 is normally operable from one side only of door 10 after the door is hung on hinges 16. However, the dual rotation feature of member 60 permits the embodiment shown by FIG- URE 3 to be used with either right hand or left hand opening doors without altering the shape or mounting means of member 60. Thus, if hinges 16 seen in FIG- URE 1 were to be removed from door jamb portion 20 and door 10 were rehung with the hinges secured to portion 24 of the door jamb, no change in the latch mechanism of door 16 would be required to adapt member 60 to the new position.

As further seen from FIGURE 3, securing means may be advantageously provided to hold member 60 in holding relationship with latch member 62. The stated means illustratively comprises a small wedge 76 inserted between door 10 and a flange portion 78 on member 60, with a dangle chain to retain the wedge when not operatively engaged as shown in FIGURE 3. Thus, after member 60 is rotated into the holding position shown in FIG- URE 3 whereby unlocking action of latch member 62 is prevented, securing element 76 may be inserted as shown to maintain member 60 in holding position. The embodiment thus shown in FIGURE 3 has the advantage of not requiring any separate mounting or bracket means for installation on existing door latches, since it may involve only removal of screw 74 from the existing coverplate and replacement of the same screw with member 60 mounted thereupon in the manner suggested by FIG- URE 3, and the 'notching of member 62 as by a hacksaw blade.

FIGURES 4 and 5 show a further structural modification differing from FIGURES 2 and 3, but embodying the same inventive principles. Thus, FIGURE 4 shows a rotatable member 88 corresponding in shape and function to rotatable latch lock 60 in FIGURE 3. Latch lock member 80 is mounted on screw 82 in the same manner as discussed above for member 60 on screw 74, however, member 80 is rotatably movable about screw 82 only a limited amount, sufi'icient to disengage or to operatively engage edge 84 of member 86 with groove 86 in latch member 62.

Combination moving and locking dual wedge means 88 are provided for application of force to cause rotation of member 80 about a center axially aligned with screw 82 to the limited extent necessary for locking engagement of member 80 with latch 62 or removal of the same from such locking engagement. Wedge means 88 may advantageously comprise a single unitary element of .generally elongate form having a substantially constant thickness and a substantially straight edge 90 adapted to bear against a surface of door 10 in sliding relationship therewith. Each end of elongate element 88 has a maximum width as shown at 92 and 94, the width sloping from these two maximums to a minimum width at a location intermediate the two stated locations as shown at 96.

In the embodiment illustratively shown by FIGURES 4 and 5, member 80 has a flange-like projecting portion 98 which may be integrally formed thereon as by merely bending the stated portion at substantially a degree angle from the remaining portion of the element. Flange portion 98 is in bearing contact with cam surfaces 100 and 102 formed on element 88 by the sloping change of width between extremities 92, 94 thereof and intermediate location 96. No other or additional holding means is necessary to retain element 88 in operative relationship with member 80 due to the cooperative shape of the two stated parts, since only limited vertical movement of element 88 is permitted after assembly of the components into the operative relationship shown by FIGURES 4 and 5 is completed. Thus, by application of force upwardly upon element 88 so as to cause sliding movement of the same relative to door 10, lower cam surface 102 will press upon lower edge 104 of flange-like portion 98 and thereby rotate member 80 into the position shown by FIGURE 4 wherein edge 84 is disengaged from groove 86 in latch member 62, and is firmly held out of engagement by the wedging action of surface 102 applying continual force to portion 98. Conversely, downward force manually applied to element 88 will result in cam surface 100 pressing upon the upper edge 106 of portion 98 and causing rotation of member 80 intothe position shown in FIGURE 5 wherein edge 84 enters within groove 86 of latch member 62, thereby preventing withdrawal of [member 62 as necessary to open door 10. It will be understood that the same movement of element 88 to rotate element 80 into the position shown by FIGURE 5 will serve to hold latch member 62 in the withdrawn position if member 62 is withdrawn as by turning the doorknob operatively connected therewith before the element 80 is rotated into the stated position.

FIGURES 6 and 7 show a further modification differing from FIGURES 2-5, inclusive, but embodying the same inventive principles. Thus, FIGURE 6 shows an exploded view of a latch holding means including rotatable member 110 corresponding generally in shape and function with member 80 shown in FIGURES 4 and 5, but without a flange-like projection 98. However, the same essential function achieved by projection 98 in FIG- URES 4 and 5 is served in FIGURES 6 and 7 by adjustably movable element 112. Element 112 is of generally elongate form having two spaced-apart bosses 114 and 116 integrally formed thereon and adapted to engage the upper and lower edges 118 and 120 of rotatable member 110 in gripping relationship therewith by the aid of clamping means which may comprise two set-screws as shown at 122 and 124. Element 112 is also grooved at 126 to receive a vertically slidable dual wedge means 128 corresponding generally in shape and function with wedge means 88 described above and shown in FIGURES 4 and 5, but further including a projecting lip or vertical stop means 130. With the foregoing parts from FIGURE 6 assembled in operative relationship as shown by FIGURE 7, element 112 is secured in adjustably fixed relationship to rotatable member 110 by tightening of screws 122 and 124 so as to be pivota'lly movable therewith about a centerline axially through screw 132.

From the above description, 'it will be understood by those skilled in the art that a firm holding force is applied by dual wedge means 88 and 128 on rotatable members 80 and 110, respectively, to hold the same either in the raised position of disengagement shown in FIGURE 4, for example, or in the lowered position of engagement with latch member 62 shown in FIGURES 5 and 7. Moreover, since door 10 is not of precisely known or uniform thickness in every case, and since mortising of a door to accommodate the door-handle and latch mechanism may produce different locations of screws 82 or 132 so that such screws may not be exactly centered between the outer and inner edges of door 10, it is a principal advantage of the embodiment shown by FIGURES 6 and 7 that element 112 may be adjustably positioned with respect to element 110 as required to achieve firm holding action of wedge means 128 no matter what the size of door or mortising inaccuracies may be.

While the particular structural details set forth above and in the drawings are fully capable of attaining the objects and providing the advantages herein stated, the stmcture thus disclosed is merely illustrative and could be varied or modified to produce the same results without departing from the scope of the inventive concept as defined in the appended claims.

I claim:

1. Mechanism for holding a pivotally mounted door in the closed position relative to an adjacent door jamb, said mechanism comprising:

latch means supported on said door proximate an edge thereof,

said latch means including an elongate bolt having a distal end projecting from said door edge and translationally movable to extend into a cavity in said door jamb,

said latch means further including at least one doorknob operatively connected to withdraw said bolt from said cavity,

a shallow groove in said bolt proximate said distal end thereof,

a coverplate mounted on said door edge by at least one mounting screw, said bolt extending through said coverplate,

independent means operatively elated to said bolt and mounted on said. door for selectively preventing the withdrawal of said bolt from said cavity by said doorknob,

said independent means comprising a rotatable element of thin-sheet form pivotally supported on said one screw for limited pivotal movement in two opposite directions about a pivot center through said one screw,

' said rotatable element having at least one edge adapted to operatively engage said shallow groove at one limit of said pivotal movement,

elongate wedge means slidably movable with respect to said door and operatively related to said rotatable element for selectively preventing withdrawal of said one edge from said shallow groove, and for selectively causing withdrawal of said one edge from said shallow groove upon the application of force to cause said slidable movement of said wedge means,

said elongate Wedge means including at least one sloping cam surface thereon, and

adjustably positionable bearing contact means secured to said rotatable element operatively related to said slidable Wedge means so that sliding movement of said slidable wedge means causes contact between said sloping cam surface and said bearing contact means to rotate said rotatable element and to selectively hold said rotatable element in said position of operative engagement between said edge and said 8 groove, said bearing contact means being adjustably positionable with respect to said sloping cam surface for establishing said contact between said contact means and said cam surface.

2. In a latch mounted on a door adjacent an edge thereof for selectively holding said door edge in close juxtaposition with a confronting door jarnb:

an elongate translationally movable bolt having a portion thereof projecting beyond said door edge and a distal end on said projecting portion operatively engageable with a cavity in said door jamb,

a recess in said projecting portion of said bolt on a surface thereof closely adjacent door edge from which said portion projects,

a cover plate mounted on said door edge by at least one screw and having a hole therein through which said bolt projects,

selectively operable holding means pivotally supported by said one screw for limited pivotal movement into and out of operative engagement with said recess for selectively preventing said translational movement of said bolt while said distal end is engaged within said cavity,

said holding means including a thin sheet element pivotally mounted on said one screw for said limited pivotal movement of said element relative to said door, said element having an edge portion movable into or out of operative engagement with said recess at the maximum limits of said limited movement, and

securing means for selectively securing said element against said pivotal movement at each of said maximum limits thereof,

said securing rneans comprising an elongate member having a bearing surface thereon slidably contacting said door,

said elongate member further having a maximum width at each end thereof and a minimum width intermediate the ends thereof thus forming two wedging portions,

said securing means including flange-like projecting means for retaining said elongate member in operative relationship therewith and for contacting one of said wedging portions firmly at each of said maximum limits of pivotal movement.

References Cited by the Examiner UNITED STATES PATENTS 1,014,583 1/1912 Eisenhart 292153 1,165,614 12/1915 McCann 292- 1,354,222 9/1920 Sibley 292-257 2,128,479 8/1938 Taylor 292207 X EDWARD C. ALLEN, Primary Examiner.

J. R. MOSES, Assistant Examiner. 

1. MECHANISM FOR HOLDING A PIVOTALLY MOUNTED DOOR IN THE CLOSED POSITION RELATIVE TO AN ADJACENT DOOR JAMB, SAID MECHANISM COMPRISING: LATCH MEANS SUPPORTED ON SAID DOOR PROXIMATE AN EDGE THEREOF, SAID LATCH MEANS INCLUDING AN ELONGATE BOLT HAVING A DISTAL END PROJECTING FROM SAID DOOR EDGE AND TRANSLATIONALLY MOVABLE TO EXTEND INTO A CAVITY IN SAID DOOR JAMB, SAID LATCH MEANS FURTHER INCLUDING AT LEAST ONE DOORKNOB OPERATIVELY CONNECTED TO WITHDRAW SAID BOLT FROM SAID CAVITY, A SHALLOW GROOVE IN SAID BOLT PROXIMATE SAID DISTAL END THEREOF, A COVERPLATE MOUNTED ON SAID DOOR EDGE BY AT LEAST ONE MOUNTING SCREW, SAID BOLT EXTENDING THROUGH SAID COVERPLATE, INDEPENDENT MEANS OPERATIVELY ELATED TO SAID BOLT AND MOUNTED ON SAID DOOR FOR SELECTIVELY PREVENTING THE WITHDRAWAL OF SAID BOLT FROM SAID CAVITY BY SAID DOORKNOB, SAID INDEPENDENT MEANS COMPRISING A ROTATABLE ELEMENT OF THIN-SHEET FORM PIVOTALLY SUPPORTED ON SAID ONE SCREW FOR LIMITED PIVOTAL MOVEMENT IN TWO OPPOSITE DIRECTIONS ABOUT A PIVOT CENTER THROUGH SAID ONE SCREW, SAID ROTATABLE ELEMENT HAVING AT LEAST ONE EDGE ADAPTED TO OPERATIVELY ENGAGE SAID SHALLOW GROOVE AT ONE LIMIT OF SAID PIVOTAL MOVEMENT, ELONGATE WEDGE MEANS SLIDABLY MOVABLE WITH RESPECT TO SAID DOOR AND OPERATIVELY RELATED TO SAID ROTATABLE ELEMENT FOR SELECTIVELY PREVENTING WITHDRAWAL OF SAID ONE EDGE FROM SAID SHALLOW GROOVE, AND FOR SELECTIVELY CAUSING WITHDRAWAL OF SAID ONE EDGE FROM SAID SHALLOW GROOVE UPON THE APPLICATION OF FORCE TO CAUSE SAID SLIDABLE MOVEMENT OF SAID WEDGE MEANS, SAID ELONGATE WEDGE MEANS INCLUDING AT LEAST ONE SLOPING CAM SURFACE THEREON, AND ADJUSTABLY POSITIONABLE BEARING CONTACT MEANS SECURED TO SAID ROTATABLE ELEMENT OPERATIVELY RELATED TO SAID SLIDABLE WEDGE MEANS SO THAT SLIDING MOVEMENT OF SAID SLIDABLE WEDGE MEANS CAUSES CONTACT BETWEEN SAID SLOPING CAM SURFACE AND SAID BEARING CONTACT MEANS TO ROTATE SAID ROTATABLE ELEMENT AND TO SELECTIVELY HOLD SAID ROTATABLE ELEMENT IN SAID POSITION OF OPERATIVE ENGAGEMENT BETWEEN SAID EDGE AND SAID GROOVE, SAID BEARING CONTACT MEANS BEING ADJUSTABLY POSITIONABLE WITH RESPECT TO SAID SLOPING CAM SURFACE FOR ESTABLISHING SAID CONTACT BETWEEN SAID CONTACT MEANS AND SAID CAM SURFACE. 